The present invention is related to nuclear reactor fuel bundles such as are used in reactors of the pressurized water or boiling water type. In such bundles, fissionable fuel is disposed within tubular fuel rods which are mounted in parallel array between a pair of end plates. When the bundle is in service in a nuclear power reactor, water passes upwardly along the outer surface of the fuel rods, receiving heat therefrom owing to the reaction occurring inside. In order to permit uniform heat removal and to avoid overheating of the tubes, it is necessary that they be accurately spaced. Maintaining the spacing of the elongated tubes in such a closely spaced array, under conditions in which vibration naturally occurs, requires a carefully designed spacer unit which has been the subject of many prior art patents. In particular, the present invention relates to the spacer described in application Ser. No. 223,528 filed Feb. 4, 1972, and jointly assigned to the assignee of the present invention. Accordingly, the earlier application is incorporated by reference into the present application.
In the preferred spacer design of the reference application, a corner mounted spring engages the side of fuel rods passing through each of the grid openings formed by the spacer and holds the fuel rod against protrusions which have been formed from the grid walls. This three-point engagement provides a stable positioning of the fuel rod within the spacer. In a typical fuel bundle there are a plurality of spacers disposed along the length of the fuel rod. In order to assure proper positioning during operation, the spacers must be secured in the desired position; otherwise, they may be displaced upwardly owing the vibration and to the flow of water adjacent the tubes. In the prior art, such spacers have been held in position by special spacer capture rods. These fuel rods are of special sectional construction which are joined by connectors which engage the spacers and hold them in position. Such construction is difficult and expensive to fabricate and increases the possibility of failure of these rods. The present invention overcomes these disadvantages, providing a simpler construction which is less expensive to fabricate and easier to assemble.